In the case of mixture generating apparatus, the injection valves used are very important, and this requires precise checking and adjustment, especially of electronically controlled injection valves. Besides combined production and testing lines for checking, adjusting and assembling valves, in which some functions are performed manually, e.g. placing valves in the test stands, automated systems are also known.
In known automated testing and assembly lines, injection valves carried on pallets are transported on conveyor devices, e.g. creeper or slatted belts, by frictional drive along a test line comprising one or more test stands. Diversion of the pallets into the test stands is done by switching points or other deflectors such as, in particular, elevatable stops or stoppers in conveyor devices that divert a pallet on to the conveyor device that runs at right angles to the main conveyor belt and leads to the test stand. With this arrangement not only is the retardation of the pallet that is being transported at high speed disadvantageous; it also does not allow the transportation time to be precisely fixed, because the acceleration of the pallets cannot be exactly determined; optimized flow of material is thus not ensured. In addition, the known test lines require a large amount of space and the distribution of the pallets and the handling in the individual test stands also requires the expenditure of a large amount of mechanical effort, with the mixing of the individual operations operating to the detriment of ease of keeping track of and servicing of the testing line.
Further not unimportant problems arise in ensuring sufficiently constant pressure and temperature, particularly between the hydraulic measurement circuits of all the test stands. The major problems result from the pulsing of the flowing test medium caused by pumps and test-pieces, and switching and acceleration operations that are involved when changing the test-pieces (in this case, valves).